In integrated acousto-optics, control of the spectral position of the Brillouin gain curve is highly desirable. In optical gyroscopes, for example, control of the spectral position of the Brillouin gain curve allows for control of the frequency detuning between clockwise and counterclockwise beams. In other integrated applications, control of the spectral position of the Brillouin gain curve allows for a spectral misalignment between the gain spectrum of the fiber used to excite the waveguides and that of the waveguides themselves, avoiding the complications their overlap would otherwise cause.
In prior approaches, the only structures that allow for control over gain spectra involve a finite number of guided acoustic modes. In these structures, changing the waveguide geometry leads to a change in the dispersion of both the optical and acoustic modes. However, structures which support guided acoustic modes generally do so at the expense of higher optical losses, and the spectral range across which such structures can tune the Brillouin gain curve remains limited.